Broken Promises
by StarrySky0103
Summary: Arianna, the sweet, younger sister of Eren Jaeger. She's loyal and always keeps her promises, doing her best to fulfill all of them. But what happens when her seemingly innocent promises slowly start to cross over, making her have to choose whose promises she should keep, putting all relationships on the line? She also holds a secret that could make or break humanity. LEVI/OC
1. Prologue

**Disclaimer: I do not own anything from Shingeki no Kyojin.**

**AUTHOR'S NOTE: Hello everyone! This is the 10****th**** story that I have published at this website! Updates are a little slow, since I try to update all of my stories, but I'll try my best!**

**WARNING: If you can't take HUGE AGE DIFFERENCES in romantic relationships, this is not the story for you, because Levi and my OC are going to be about 9 years apart, considering that my OC is Eren's little sister. But if you're fine with that, then I hope you enjoy the story!**

* * *

**"If you lose, you die.**

**If you win, you live.**

**If you don't fight, you can't win!"**

**-Eren Jaeger**

* * *

**PROLOGUE**

"Oh, honey, look, she's beautiful," Carla Jaeger told her husband, Grisha. Grisha held a one year old boy in his arms as he leaned over to take a look at his new daughter. He smiled.

"She is indeed, just like you." Then the baby's sea green eyes turned into a dark purple. The two blinked in surprise.

"Her eyes… changed color?" Carla asked, confused. Grisha looked as calm as ever.

"She's special," were his only words.

_That was the day I was born and the first time that my parents discovered my unusual colored eyes that changed depending on my emotions_

* * *

"Onii-chan! Give it back!" a childish and girly voice exclaimed. Eren came running down the stairs and ran to the other side of the room. Not too long after him came out a little 6-year-old girl with her ebony hair in two loose pig tails. Her teary eyes were a mixture of orange and blue. "Mama! Eren took away my doll!"

"Tattletale!" Eren screamed. She stuck her tongue out at him. Carla smiled at the sight of her two children.

"Eren, give back Aria's doll," she reprimanded.

"She was being annoying!" he retorted.

"Was not!"

"Was too!"

"Was not!"

"Was too!"

"Okay, okay. Kids, calm down." Carla placed a hand on each of their backs. "Both of you apologize."

"But it wasn't my fault!" the two yelled in unison before glaring at each other.

"Kids," she said in a warning tone. They pouted before turning to each other.

"I'm sorry for taking your doll."

"I'm sorry for being annoying." The two smiled happily.

"Do you want to go outside and play?"

"Yeah!" Carla chuckled at her children's childishness.

_I love my brother, Eren. He's such a hothead and can be kind of a jerk sometimes, though._

* * *

Aria sobbed as she crouched in a fatal position, three boys towering over her. "Come on, get up."

"You're such a weakling!"

"What's up with her eyes?! They're so creepy."

"Hey!" an enraged voice screamed. The boys turned to see a furious Eren charge towards them.

"Heh, look it's Eren! He thinks he can beat us with those scrawny arms of his!" Eren ran and threw punches and kicks that they easily returned with their own. Eren was obviously overpowered, but he didn't seem to care. He continued to fight until the boys finally left. He panted before running over to Aria.

"Are you alright, Aria?" he asked worriedly. She nodded then sniffled. Eren took her in his arms and let her cry. "I'll always protect you Aria."

_Whenever I was bullied, Eren would always come to help me. Even though it was painfully obvious that he wouldn't win, he never gave up._

* * *

Eren and Aria knocked on the door and a man opened it. He scowled. "How the hell did you get here?!" They both looked down.

"We just got lost and w-wanted to find shelter." The man turned back to his friend that gave him a signal. He nodded and turned back with a smile.

"Now, kids shouldn't be walking alone in the forest. There are scary wolves out there. But it's fine now. Just come with me and-" He didn't finish his sentence, for Eren had stabbed him in the heart. Aria flinched slightly at Eren's unhesitant move.

"Thanks, mister. I understand. Now… Die, asshole!"

"No way!" The two mysteriously closed the door. The other man quickly went out in the hall to look for them. But as he walked out, Aria slashed his neck with a long blade. The third and only other one in the room backed away. Eren charged and stabbed him with a long spear.

"Die, you bastard! This is what you guys get! Don't ever stand up again!" Aria stood behind him.

"Onii-chan, that's enough!" He finally stopped and panted. The girl, Mikasa, watched with blank eyes. They released her from the ropes around her wrists.

"I'm Eren and this is my sister, Aria. We're Doctor Jaeger's kids. You're Mikasa, right? We went to your house for a check-up." Then she said something that made the siblings' blood run cold.

"…There were four of them." They turned as they heard a clatter and saw the fourth man standing behind them. Eren lunged for the knife, but was kicked away. The man grabbed the two and placed them in a chokehold.

"Fight!" Eren managed to say.

"Eh?"

"Fight," Aria repeated. "If you lose, you die."

"If you win, you live."

"IF YOU DON'T FIGHT, YOU CAN'T WIN!" they screamed in unison. Mikasa shakily grabbed the knife.

"B-but… I can't do… something like that." Then she felt a new emotion rise within her. She suddenly stopped shaking. She ran forward with a cry.

The Military Police checked the damage. "They were killed by those three children."

"Seriously?"

The three kids stood outside. Eren and Aria stood in front of their father. "What were you two thinking?!" Eren and Grisha started to yell at each other while Aria looked at her feet.

"We just wanted to save her," Eren said with tears in his eyes. Grisha sighed then turned to Mikasa.

"Do you remember me? We met a few times."

"…Doctor Jaeger, where should I go from here… I'm so cold…" Eren and Aria glanced at each other before walking up to her. Eren wrapped a scarf around her head while Aria placed fake leather gloves, which were open at the fingers, on her hands.

"Here, now you're not cold, right?"

"With these, you'll always be warm." Mikasa stared, wide-eyed before nodding.

"Mikasa, come live with us. You've been through a lot. You need plenty of rest." She looked at the two.

"What is it?" Eren asked while Aria tilted her head. They each grabbed one of her hands.

"Come on, Mikasa-chan," Aria said. "Let's go back to our home." Tears ran down Mikasa's face before nodding.

"Let's go home…"

_That was the first time I, or any of us, killed someone. It was also the day when I got a new friend._

* * *

"Mom!" Eren and Aria screamed in horror as they watched their own mother be eaten in front of them.

_ A Titan that was over 50 meters tall had broken the wall that day. I lost my beloved mother and never saw my father. Eren, Mikasa, Armin, and I safely escaped. That was also the last day that I called Eren, Onii-chan, with a few exceptions._

* * *

"I, Keith Shadis, am your instructor! Will you all become Titan food?! Or become glorious soldiers that defend mankind?! I will judge you!" Aria stood with Eren next to her, her eyes a stunning sea-green that shined with confidence.

_That was the day that I decided that I wanted to save humanity, alongside my brother, Mikasa, and Armin._

* * *

"Tch, stubborn brat," a short man grumbled.

"Corporal Levi, I don't care what you say! I'll love you no matter what and you can't do anything abou-" Aria was cut off as Levi grabbed her by the arm and slammed his lips to her own.

_That was when I admitted my love for a harsh and stubborn midget corporal._

* * *

**_"Hey, Aria, we'll always be together right?"_**

**"Of course, Eren. You're my brother."**

**_"Aria, promise me that you'll always help me protect Eren."_**

**"Who do you think I am, Mikasa? I won't let anyone hurt a hair on my brother."**

**_"Arianna, will you do me a favor? No matter how bad the situation, please be there to support me and have my back."_**

**"Duh, Annie. That's what friends are for!"**

**_"Oi, brat… You better always be by my side. You're mine and no one else's."_**

**"I will, Levi. I love you."**

_I made so many promises… that I just couldn't keep…_

* * *

_ This is the story of me, Arianna Jaeger. My friends. My family. The love of my life. My tears, my laughs… __**And all of my broken promises.**_

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**AUTHOR'S NOTE: How was it? If you liked it, FOLLOW, FAVORITE, AND REVIEW! If you like my writing, please check out my other stories.**

**_Rulers of the Underworld_****_ LEVI/OC (Shingeki no Kyojin/Attack on Titan Fanfic)_**

**_Dreams of Despair_****_ TOGAMI/OC (Dangan Ronpa Fanfic)_**

**_My Small World_****_ SHIKI/OC/ICHIJOU (Vampire Knight Fanfic)_**

**_Revenge is a Dish Best Served_****_ OC/? (Fullmetal Alchemist Fanfic)_**

**_Polar Opposites_****_ OC/? (Prince of Tennis Fanfic)_**

**_Psychotic Beauty_****_ ATOBE/OC (Prince of Tennis Fanfic)_**

**_P.S. I Hate U_****_ KIRIHARA/OC (Prince of Tennis Fanfic)_**

**_Caged_****_ FEM!ATOBE/? (Prince of Tennis Fanfic)_**

**_No Regrets _****_OC/? (Prince of Tennis Fanfic)_**

**Also, these are Aria's eye colors depending on her mood.**

** Silver: Scared**

** Black: Blank, emotionless**

** Purple: Excited, happy**

** Blue: Sad, depressed**

** Green: Envious**

** Sea-green: Normal**

** Yellow: Pained (Physically, Emotionally, Mentally)**

** Orange: Angry **

** Pink: Shy, flustered, embarrassed**

** Red: ?**

**The color is deeper the more she feels that emotion. Sometimes, she may have specks of one color within a main color, colors mixed together, or just one color. The deeper and more of the color, the stronger she feels that mood.**


	2. Chapter 1: The Undesired Day

**Disclaimer: I do not own anything from Attack on Titan/ Shingeki no Kyojin.**

**AUTHOR'S NOTE: Hey, guys! Thank you so much for your reviews! I'm so happy that you guys liked the prologue. I can't believe that I got so many reviews on just the prologue, but I guess that means I'm doing something right! Well, enjoy this chapter!**

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**"Nothing can suppress a human's curiosity."**

**-Grisha Jaeger (Attack on Titan/Shingeki no Kyojin)**

* * *

**CHAPTER 1: THE UNDESIRED DAY**

Eren abruptly woke up to the faces of Mikasa and Aria. "Mikasa… Aria?"

"Eren, you're crying." He immediately denied it. Aria rolled her currently sea green eyes.

"Come on, we have to go home." As the three walked home, they ran into members of the Garrison, one of the three branches of the military. They were drunk and playing cards. Eren frowned.

"If you guys are drinking and fooling around like this, then how are you going to fight?"

"Eh?" Hannes looked confused. "When are we going to have to fight?"

"When the Titans break down the wall!" Eren screamed. Aria gave him a warning look, but he continued to talk. "My dad said that when people are the most relaxed, bad things start to happen!

"Dr. Jaeger said that? We do owe him a lot from saving this town from the plague, but Eren, when soldiers are fighting, the citizens know that something bad has happened. So they're much happier when we're sitting here drunk and doing nothing."

"Yeah, we might not get out of these walls. We could live as long as we eat and drink. But then we're living like… like livestock!" Hannes looked surprised while the others just laughed. As they walked away, Hannes thought to himself.

"That kid… Don't tell me he's planning on joining the Survey Corps…"

* * *

"Eren, I think you should give up on the Survey Corps," Mikasa suggested.

"What? You think they're stupid too?" he asked, incredulously.

"That's not what I meant. It's just-" She was cut off when the large bell rang, signaling the return of the Survey Corps. A smile spread across Eren's face and even Aria couldn't suppress the slight twitch of her lips. She may not show it as much as her brother, but she also admired the Survey Corps and their bravery.

"Come on! The heroes returned!" The three watched as the Survey Corps walked in, with a considerably less amount of people, Aria noticed. Eren gasped in horror when he saw all the injured soldiers and grim faces. Aria closed her eyes with a pained expression as a woman received her son's arm as the only thing that was salvaged of him.

"But my son… he was useful right? He may not have been a hero… but he at least died helping humanity fight back, right?!"

"O-of course! No… During this mission… Even after all of our missions… We have not made any progress what so ever! I'm a failure! I've just gotten soldiers killed left and right! And we haven't learned anything useful about the Titans!"

* * *

"We're home!" Carla turned and gave her kids a smile.

"Welcome home. Oh, Eren, you surprisingly have a lot of wood today."

"Y-yeah." Carla pulled on his ear.

"Hey!"

"Your ear was red. Proof that you were lying. Mikasa and Aria helped you, didn't they?" Aria giggled.

"Eren, you're so easy to read." She looked at her father, Grisha, as he placed things in his bag. "Are you going somewhere for work?"

"I have to meet with someone in the inner walls. I'll probably be back in two or three days." They were eating dinner when Mikasa spoke.

"Eren wants to join the Survey Corps." The room went silent.

"Mikasa, I told you not to tell!" Carla rushed over to her son.

"Eren, what are you thinking?! Do you know how many people die outside those walls?!"

"I know! But Aria's been thinking about it too!"

"What?! Aria, is that true?!" Aria bit her lip and glared at Eren.

"Yes, but Mom, please understand-"

"No, why-"

"Eren, Aria," Grisha interrupted, "why do you want to go outside?"

"I want to see and understand the world outside. I don't want to die inside these walls without knowing what's out there!"

"And if no one takes on their jobs," Aria continued quietly, "…Then all those who lost their lives would have died in vain." Grisha didn't say anything and stood up.

"My ship's here. I have to get going."

"Wait, help me convince these two!"

"Carla, nothing can suppress a human's curiosity. And Eren, when I get back, I'll show you the basement that I've been keeping from you." He showed him the golden key that was around his neck and Aria subconsciously grabbed her own silver key necklace. She remembered when Grisha gave her that key.

* * *

_ "Aria, I want you to have something," Grisha told her. She looked up, confused._

_ "What is it?" He took something out of his pocket. It was a beautiful, silver key on a silver chain. Aria's eyes shifted into a deep lavender. "It's so pretty! What does it open?" He showed her a book with a lock on it. "A diary?" He shook his head._

_ "It's a book filled with information about something that will most likely affect you, Eren, and humanity. It will change your life. Read it when this happens."_

_ "But what exactly is going to happen?" she asked._

_ "You'll know when it happens. Something will happen to both you and Eren, but this book is mostly for you. Keep this with you always." Aria was confused, but she just nodded her head._

* * *

Ever since that day, Aria always kept the key around her neck and the book, still unopened, in a satchel that she carried around.

"Well, I'm leaving," Grisha said. And with that, he was gone.

"I won't allow it. You won't be joining something as stupid as the Survey Corps," Carla concluded.

"Stupid? I think people who are content living like livestock are more stupid!" Eren screamed before running off.

"Eren!"

"Mom," Aria began, "I know that you're worried, but Eren and I want to be able to change the world. We want to be able to change humanity… I hope one day you'll be able to see it the way we do," she finished before running after Eren. Mikasa eventually caught up to her and the two chased after Eren. He was about to get in a fight with the resident bullies when they caught sight of Mikasa and Aria running behind them, faces resembling the devil himself.

"I-it's Mikasa and Aria! Run!"

"Heh," Eren laughed. "They ran after seeing me!"

"No," the blond boy who was being bullied said, "they were running from Mikasa and Aria." He flinched as he tried to get up. Aria placed an arm around his shoulders.

"Are you alright, Armin?"

"…I can get up by myself."

* * *

"So, when I told them humanity had to go outside eventually, they beat me up, calling me a heretic." Eren threw a rock into the lake.

"Tch, why does everyone hate us so much for wanting to go outside?"

"Well, it's inevitable. These walls have protected us for over a century. It's been peaceful… No one wanted to risk the Titans entering the walls when someone goes out. That's why the King's government banned people from showing interest in the outside world," Armin explained.

"People are insane," Aria stated. "They think that these walls will always be here to protect us. Although the walls have been intact for the past 100 years… there's no guarantee that they won't be broken down today."

A loud rumble reverberated through the town of Shiganshina. The four kids looked confused. "An earthquake?" They turned to look at the wall that had protected them from Titans for the past century and found that their guess was far off. Their eyes widened as they saw a gigantic hand grab onto the wall. A face slowly revealed itself. Aria gaped and her eyes turned into a shining silver.

"I-impossible! That wall is 50 meters tall!" The Titan pulled his foot back and slammed it into the wall, creating a giant hole. Chunks of the wall went flying throughout the town and people screamed as they attempted to avoid them. Eren and Aria looked at each other.

"Mom!" they said in unison. The two siblings set off for their house that was located near the wall and Mikasa followed suit.

"Wait!" Armin reached out a trembling arm to stop them, but forced it back down with his other one. "It's too late… This town… has been overrun by Titans!" he shouted as tears streamed down his face.

* * *

The three ran, ran like it would be the last thing that they would ever do… And it just may be. Aria shut her eyes and took in a shaky breath.

_'Mom… please be alright…'_

* * *

When the three found their house, they were horrified to see it in ruins. "Where's Mom?!" They caught sight of Carla underneath all the rubble and the three attempted to lift the destroyed roof off of her.

"I want you three to run!" she screamed as a Titan started to walk towards them.

"No, we can't do that!" Aria cried, tearfully.

"We're going to escape together!" Eren declared.

"Listen to me! My leg was crushed under all the rubble. Even if I was able to get out, I wouldn't be able to run with you." The three refused to believe it. Hannes then dropped down next to them. "Hannes! Get the kids away from here!" He smiled.

"Carla, I'm gonna save all four of you." He took out his blades and charged at the Titan then abruptly froze. He stared wide-eyed at the sadistically smiling Titan before sheathing the blades and running back. He grabbed the three children and ran, leaving Carla behind.

"WAIT! No! What about Mom?!" Aria's silver eyes watched in horror as she saw her own mother being devoured by a Titan. Her lips parted and she let out a bloodcurdling scream. Aria jumped out of his arms and ran back to where the Titan was.

"Wha-?!"

"ARIA!" Eren and Mikasa shouted. Hannes cursed. He didn't have time to go back for Aria.

"Hannes-san! Let us down! ARIA! ARIAAA!" Eren called as his sister's figure started to fade away.

Aria ran. She didn't know what the hell she was doing. She didn't know what the hell she was _thinking. _She couldn't take on a Titan. As she got closer, she finally realized how stupid her idea really was. She paled and started to run in a different direction. The Titan that ate her mother hadn't noticed her. But as she turned a corner, she gasped. A 12-meter-Titan towered over her. She slowly backed away until her back hit a wall. Her breath started to get uneven as she realized that this was the end. The Titan picked her up in its large hand. The Titan's grip was surprisingly gentle. When she didn't feel herself being ripped to pieced, she hesitantly opened her eyes. She flinched at the Titan's gaze. It wasn't sadistic. It seemed curious, almost… confused.

But she didn't have time to ponder over the subject. A green blur flew by and all of a sudden, Aria felt herself plummeting to the ground. Aria's eyes shot up, for she was being carried bridal-style, to see a short man with a heated glare. He had cropped, black hair and cold, gray eyes. She recognized the 'Wings of Freedom' that adorned his green cloak.

"Oi, brat. Hold on tight," he warned.

"Eh?" Then he swung towards the Titan. Aria shrieked and clung tightly onto the man as he roughly maneuvered the gear and expertly sliced the Titan's neck. Blood splattered on her cheeks and the Titan fell forward with a groan. Her arms were wound tightly around the man's neck as he used his 3DMG to swing towards the escape boats. "T-thank you…" she whispered.

"Tch," was his only reply.

"What's your name?" He looked down at her. He was about to spout out another insult when her eyes changed from silver to a dark sea-green. She was confused to see the slightly shocked expression on her savior's face then realized it must have been her odd eyes. She looked down insecurely and he sighed.

"Levi."

"Eh?"

"My name is Levi." She blinked before smiling.

"Arianna… Arianna Jaeger." He didn't say anything more. When they arrived at the boats, he gently let her down and started to walk away. "Levi!" she called. He turned with a raised eyebrow. "I'm gonna join the Survey Corps! We'll meet again someday!" He appeared taken aback for a few seconds before his lips twitched upwards in an amused smirk.

"Do whatever you want," he said and swung out of sight. Aria boarded the boat and was able to meet up with her brother and two friends. When Eren saw her, he was furious.

"What the hell were you thinking?!" he demanded.

"I'm sorry… I didn't know what I was doing… But I was saved by someone from the Survey Corps." Eren sighed before pulling her into a loving embrace.

"Don't ever do something reckless like that ever again." Aria laughed.

"You're the last person I want telling me that." Eren released her then slammed his hands on the railing.

"I'm gonna kill every single Titan out there… There won't be a single one of them left on this Earth!" Aria stood by him, as she had always done. He turned to her. **_"Aria, we'll always be together, right?"_**She smiled.

**"Of course, Eren. You're my brother."**

* * *

**_That was my first promise…_**

**_One that I never expected to not be able to keep…_**

* * *

**AUTHOR'S NOTE: So, how was it? If you liked it, FOLLOW, FAVORITE, and, REVIEW! I tried to add in some Levi, because it'll be hard to get him in for the next couple of chapters during training and stuff. I hoped you all liked it!**

**Color Code for Aria's Eyes:**

**Silver: Scared**

** Black: Blank, emotionless**

** Purple: Excited, happy**

** Blue: Sad, depressed**

** Green: Envious**

** Sea-green: Normal**

** Yellow: Pained (Physically, Emotionally, Mentally)**

** Orange: Angry **

** Pink: Shy, flustered, embarrassed**

** Red: ?**


End file.
